Enoxaparin sodium is primarily metabolized in the liver by desulfation and/or depolymerization to lower molecular weight species with much reduced biological potency. Renal clearance of active fragments represents about 10% of the administered dose and total renal excretion of active and non-active fragments 40% of the dose.
The effect on hemostatic variables by dextran 70, enoxaparin and their combinations, given in doses of 500 mL i.v. and 40 mg s.c. respectively, was studied in a randomised cross-over fashion in twelve healthy male volunteers. Antifactor-IIa activity, antifactor-Xa activity, APTT, factor VIII, vWF, bleeding time and blood counts were analysed over a 24-hr period. Dextran alone did not affect antifactor-IIa activity and antifactor-Xa activity. No difference in antifactor-IIa and antifactor-Xa activity was found for Amax, tmax, AUC0-8 hr and AUC0-24 hr in the groups treated with enoxaparin or the combination of enoxaparin and dextran. Only minor changes in APTT were observed without statistical significance between the treatment groups. Factor VIII did not change significantly in the three treatment groups. However, vWF was significantly reduced in the dextran and the dextran/enoxaparin group (p = 0.046 and 0.01 respectively) but no difference was found between the two groups. Bleeding time was not significantly increased four hours after administration of the test substances and no difference was found between the individual treatment groups. /These/ findings indicate that dextran can be combined with enoxaparin, when used in thromboprophylactic doses, without increased risk for bleeding.
To largely neutralize the effects of enoxaparin following overdosage, the dose of protamine sulfate is determined by the administered dose of the low molecular weight heparin, the time elapsed since the drug was given, and blood coagulation studies. The dose of protamine sulfate to be given should be equal to that of the administered enoxaparin sodium dose if enoxaparin was administered in the previous 8 hours (ie, 1 mg of protamine sulfate should be given to neutralize 1 mg of enoxaparin sodium). If more than 8 hours has elapsed since enoxaparin was administered, an infusion of 0.5 mg of protamine sulfate may be given for each 1 mg of enoxaparin sodium administered. If the activated partial thromboplastin time (aPTT) measured 2-4 hours after the first protamine infusion remains prolonged, a second dose of 0.5 mg of protamine sulfate may be given for each 1 mg of enoxaparin sodium administered. Protamine administration may not be required if more than 12 hours has elapsed since administration of enoxaparin. However, even after higher dosages of protamine sulfate, the aPTT may remain more prolonged than would be the case following treatment of overdosage of conventional unfractionated heparin since anti-factor Xa activity is never completely neutralized. A maximum of about 60% of anti-factor Xa activity is neutralized with protamine sulfate administration for overdosage of enoxaparin.
Particular care should be taken to avoid overdosage with protamine sulfate. Administration of protamine sulfate can cause severe hypotensive and anaphylactoid reactions. Because fatal reactions, often resembling anaphylaxis, have been reported with protamine sulfate, it should be given only when resuscitation techniques and treatment of anaphylactic shock are readily available. For additional information consult the labeling of protamine sulfate injection products.
/SRP:/ Immediate first aid: Ensure that adequate decontamination has been carried out. If patient is not breathing, start artificial respiration, preferably with a demand valve resuscitator, bag-valve-mask device, or pocket mask, as trained. Perform CPR if necessary. Immediately flush contaminated eyes with gently flowing water. Do not induce vomiting. If vomiting occurs, lean patient forward or place on the left side (head-down position, if possible) to maintain an open airway and prevent aspiration. Keep patient quiet and maintain normal body temperature. Obtain medical attention. /Poisons A and B/
/SRP:/ Basic treatment: Establish a patent airway (oropharyngeal or nasopharyngeal airway, if needed). Suction if necessary. Watch for signs of respiratory insufficiency and assist ventilations if needed. Administer oxygen by nonrebreather mask at 10 to 15 L/min. Monitor for pulmonary edema and treat if necessary ... . Monitor for shock and treat if necessary ... . Anticipate seizures and treat if necessary ... . For eye contamination, flush eyes immediately with water. Irrigate each eye continuously with 0.9% saline (NS) during transport ... . Do not use emetics. For ingestion, rinse mouth and administer 5 mL/kg up to 200 mL of water for dilution if the patient can swallow, has a strong gag reflex, and does not drool ... . Cover skin burns with dry sterile dressings after decontamination ... . /Poisons A and B/
Pharmacokinetic trials were conducted using the 100 mg/mL formulation. Maximum anti-Factor Xa and anti-thrombin (anti-Factor IIa) activities occur 3 to 5 hours after SC injection of enoxaparin. Mean peak anti-Factor Xa activity was 0.16 IU/mL (1.58 mcg/mL) and 0.38 IU/mL (3.83 mcg/mL) after the 20 mg and the 40 mg clinically tested SC doses, respectively. Mean (n = 46) peak anti-Factor Xa activity was 1.1 IU/mL at steady state in patients with unstable angina receiving 1 mg/kg SC every 12 hours for 14 days. Mean absolute bioavailability of enoxaparin, after 1.5 mg/kg given SC, based on anti-Factor Xa activity is approximately 100% in healthy subjects.
A 30 mg IV bolus immediately followed by a 1 mg/kg SC every 12 hours provided initial peak anti-Factor Xa levels of 1.16 IU/mL (n=16) and average exposure corresponding to 84% of steady-state levels. Steady state is achieved on the second day of treatment.
Enoxaparin pharmacokinetics appear to be linear over the recommended dosage ranges. After repeated subcutaneous administration of 40 mg once daily and 1.5 mg/kg once-daily regimens in healthy volunteers, the steady state is reached on day 2 with an average exposure ratio about 15% higher than after a single dose. Steady-state enoxaparin activity levels are well predicted by single-dose pharmacokinetics. After repeated subcutaneous administration of the 1 mg/kg twice daily regimen, the steady state is reached from day 4 with mean exposure about 65% higher than after a single dose and mean peak and trough levels of about 1.2 and 0.52 IU/mL, respectively. Based on enoxaparin sodium pharmacokinetics, this difference in steady state is expected and within the therapeutic range.
来源:Hazardous Substances Data Bank (HSDB)
吸收、分配和排泄
抗凝血因子Xa活性的分布容积大约为4.3升。
The volume of distribution of anti-Factor Xa activity is about 4.3 L.